This invention relates to a filter holder useful in the filtration of intravenous fluids as they are supplied to patients undergoing intravenous therapy. More particularly, the invention relates to a holder for a microporous membrane filter adapted to separate gases and liquids while performing the filtration function.
Filter holder designs adapted to separate liquids from gases entrained therein while filtering the liquid are known. Specific designs for such filter holders are shown, for example, in U.S. Pat. Nos. 3,523,408; 3,631,654; 3,854,907 and 4,521,182.
It is necessary to remove air from intravenous fluid before the fluid enters the vein of a patient since bubbles which enter a vein can cause an air embolism with substantial danger of death to the patient. For this reason, filters which perform a liquid-gas separation have found particular application in the in-line filtration of intravenous fluids, i.e., filtration as the fluid is being supplied to the patient.
In general, the liquid containing gases entrained therein is supplied to a chamber having an inlet and an outlet. The outlet is separated from the inlet by a filtration material which is hydrophilic, i.e., wetted by the aqueous liquid. The typical small pore size of the hydrophilic filter prevents gas from passing through the filter at the usual operating pressures. Thus, the gas is retained in the housing while the liquid passes through the filter to the outlet. Often the filter device has a second outlet which is covered by a second filtration material which is hydrophobic, i.e., which is not wetted by the liquid. Pressure within the chamber will tend to force gas which is retained by the hydrophilic filter through the second filtration material which thus acts as a gas vent.
For example, to prepare an in-line intravenous filter for use on a patient, air must be purged from the filter chamber and connected tubing in a priming procedure Of particular importance is the removal of air which is in the tubing and filter device downstream of the hydrophilic filter. Whereas air which remains upstream of the hydrophilic filter will be retained by the filter, any air which remains downstream can pass unimpeded into the blood stream of the patient.
The filtration material typically is supported on an array of small ribs and channels which are formed in the chamber wall. In use, the channels conduct the filtered liquid to the outlet. During priming, the liquid displaces air from within the filtration material and first forms droplets on the downstream surface of the filtration material. A droplet often fills the cross-section of a channel without displacing all the air from that channel. Thus, small air bubbles may remain in the array of channels. The standard procedure for priming the prior art intravenous filtration devices is to fill the device with solution in its in-line (hanging) position, i.e., with its inlet at the top and outlet at the bottom. When the device fills with liquid upstream of the hydrophilic filter, it is inverted to purge from the device any remaining air which is located downstream of the hydrophilic filter. Small gas bubbles trapped in the narrow channels do not dislodge easily, which wastes liquid and time. Sometimes additional manipulation, such as tapping on the housing be required to dislodge the bubbles.
Accordingly, it would be desirable to provide a filter device for liquids such as intravenous fluid which is self priming whereby gas is eliminated rapidly from its interior. In addition, it would be desirable to provide such a device which is made in one piece, does not require additional supporting devices and which has a small hold-up volume.